Cross patterns

This task is about rules for growing number patterns.
A cross shape was drawn in different sizes. The first two are shown. The cross with a side length of 1 has an area of 5 cm2 and the cross with a side length of  2 has an area of  20 cm2.
Here is a table for the area of crosses which have different side lengths. 

Side length of the cross (in cm)

1

2

3

4

5

10

Area of the cross (in cm2)

5

20

45

80

125

500

Question 2Change answer

a) Explain in your own words a rule for getting the area of a cross.

Question 1Change answer

b)  Complete this rule below relating the area (a) of the cross to the length of the sides (n).
a = cm2
Published on https://newzealandcurriculum.tahurangi.education.govt.nz